1. Field of the Invention
The present invention relates generally to a single plate construction compact optical correlator which utilizes a matched filter memory to provide identification and aspect information about an input image.
More particularly, the subject invention relates to a single plate construction compact optical correlator as described in which the construction, fabrication and alignment of several of the critical optical components of the correlator should be simplified.
2. Discussion of the Prior Art
A matched filter optical correlation system is disclosed in U.S. patent application Ser. No. 814,209, filed Dec. 27, 1985. The optical correlation system disclosed therein optically compares an input image with optical information stored in a matched filter or multiple matched filters to provide identification, position, and aspect information about the input image. In one disclosed embodiment, the input image is directed onto a spatial light modulator to spatially modulate a coherent beam of radiation. The spatially modulated radiation beam is directed onto a glass photographic plate having recorded thereon a multiple holographic lens which performs a multiple number of Fourier transformations thereon to obtain an array of a multiple set of Fourier transforms of the spatially modulated radiation beam. A corresponding array of matched filters recorded on a second glass photographic plate has the array of Fourier transforms incident thereon, with each matched filter comprising a Fourier transform hologram of a scale or an aspect view of an object of interest. Each matched filter passes an optical correlation signal in dependence upon the degree of correlation of the Fourier transform of the spatially modulated radiation beam with the Fourier transform hologram recorded thereon. An inverse Fourier transform lens receives the optical correlation outputs of the array of matched filters, and performs an inverse Fourier transformation thereon. A detector detects the inverse Fourier transforms of the optical correlation outputs, and produces a detector output signal representative thereof.
One problem with this type of optical correlator is that of obtaining a proper and precise positional alignment and mounting of the glass plate having the multiple holographic lenses recorded thereon with respect to the glass plate having the multiple matched filter recorded thereon. Each holographic lens should be precisely aligned with respect to its corresponding matched filter with a typical tolerance of less than one micron.
Moreover, the alignment and mounting problems are such that the second glass plate having the multiple matched filters recorded thereon is normally used only in combination with the multiple holographic lens glass plate which was used for its fabrication and recording. In view thereof, as a practical matter, a multiple matched filter plate is normally paired with the multiple holographic lens plate which was used for its fabrication and recording, and the pair of glass plates are maintained and used together.
Another problem with this type of optical correlator is that of maintaining the precisely mounted and aligned optical components stably in position, free of extraneous movements and vibrations, particularly during usage and operation of the optical correlator. Accordingly, the optical correlator is frequently mounted and operated on a stable optical bench or table to isolate it from any extraneous vibrations and to maintain the stability and alignment of its rather precise optical components.
A further problem with this type of optical correlator is that of maintaining the precisely mounted and aligned optical components in a temperature stabilized environment such that thermal gradients do not destabilize the optical correlator.
An additional problem with this type of optical correlator is the generally large size of the overall correlator arrangement which is normally spread across the top of a stabilized optical bench or table, with the large size generally inhibiting practical applications of the correlator.